This invention relates to the field of energy reflecting devices of the type capable of reflecting incident electromagnetic energy residing in two or more segregated portions of the electromagnetic spectrum.
In order to simulate the appearance of a spacer satellite target during, for example, the testing or evaluation of a space weapon system, it is desirable to have a simulation target of known location and characteristics continuously available in space. For reasons of cost, reliability, and maintenance inaccessibility it is desirable for this simulated target to be physically rugged, simple in design, easily deployed and of sufficient mass to have a usably long space orbit life or good space kinematics. It is also, of course, desirable for such a simulated target to have thermal characteristics which make it relatively immune to solar radiation heating and weapon system heating that may be received from either friendly or hostile sources--for at least some minimum time interval. In addition to this thermal weapon immunity, it is also desirable for a simulation target to be as hardened against other forms of weapons, such as explosive devices, as is reasonably feasible--at least to the extent of being physically rugged and as simple as possible in concept. The desirability of achieving an attack-hardened target simulation device and the need for an appreciable target mass combine to diminish the capability of previously used inflated structures or balloon device targets for filling the present need.
The features of passive or energy reflecting nature in preference to an energy sourcing nature and the ability to respond to incident radiation energy in several portions of the electromagnetic spectrum are also desirably incorporated into such a simulation satellite target. Multi-spectral capability in such a target can, for example, permit radar coarse tracking and location of a target in addition to laser illumination and laser fine tracking during a final aiming or approach maneuver. The passive nature of such a satellite also desirably eliminates the need for on-board energy sources, electronic components and other complexities. The desired responsiveness to laser radiation also enables use of a simulated target with earth-situated high resolution precision tracking optical systems. For such laser tracking uses it is desirable for a satellite simulated target to provide a high degree of baffling or interference shielding between adjacent discrete reflecting locations in order that light wave interference effects between adjacent reflecting locations be minimized.
With regard to space orbit kinematics, it is of course desirable for a target simulation satellite to remain stable in either a fixed location or a predictable movement path for reasonable periods of time-in order that the cost of fabricating and disposing the satellite in space be spread over a large number of use events. Flexible launching capability such as the ability to employ leftover space in a plurality of different launch vehicles is of course a desirable feature for a simulated target device. The present-day American space program practice of reusing a launch vehicle, i.e., the advent of the space shuttle transport, offers a particularly attractive means for locating targets of this type in a selected orbital position. In particular, the presence of standard module launch apparatus in the space shuttle vehicle, i.e., the "get-away special" launch packages is well suited to space locating satellite devices or simple space targets (SST's) of this nature.
The patent are includes several examples of target devices capable of responding to electromagnetic radiation by returned signals and other response modes. Included in this art is the patent of E. R. Gill Jr., U.S. Pat. No. 3,200,400, which discloses a target capable of acting as a universal direction reversing device for both light and high-frequency electronics waves of the radar type. The Gill invention contemplates the use of sheet material having a mosaic pattern of triangular triple mirror faces in order to achieve universal energy direction reversal through a large variation of energy incidence angles. The reflecting surface in the Gill patent is a relatively thin layer of textured material.
The patent of E. F. Kingsbury, U.S. Pat. No. 3,020,792, describes an optical or radio wave apparatus for supplying, reflecting and detecting electromagnetic radiation--an apparatus that is especially intended for use in an object locating or distance measuring system. The Kingsbury apparatus also includes use of infrared spectrum radiation and a retrodirective reflector comprised of three perpendicular oriented mirrors. The source and receptor portions of the Kingsbury apparatus are shown to employ parabaloidal glass mirror members as energy reflectors. The retrodirective perpendicular mirror reflector arrangement in the Kingsbury patent is described principally as an optical device without the capabiliy for simultaneous reflections of radio frequency and optical spectrum energy.
The patent art also includes the concave polyhedral reflector structure of M. G. Chatelain, shown in U.S. Pat. No. 3,153,235. The Chatelain apparatus concerns a satellite reflector capable of returning incident radiant energy toward the energy source using a plurality of satellite reflecting points as opposed to the one single reflecting point relied upon in a conventional spherical reflector. The Chatelain apparatus also contemplates use of a closed skin surface that is inflated to become rigid. The Chatelain invention also supplements the dimpled reflector surface with a variety of adjacent geometric shapes.
Dimpled surface reflectors are also disclosed in a pair of patents issued to J. B. Brauer, U.S. Pat. Nos. 3,310,804 and 3,365,790, that are principally concerned with isotropic microwave reflection employing corner reflecting structures dispersed over the surface of a geometric shape, such as a sphere.
Corner cube reflector structures are also shown in a plurality of configurations and uses in a group of patents which are of principal interest as general background for the present invention; these patents include the signal lantern of J. C. Stimson, described in U.S. Pat. No. 1,878,909; the inflatable eight-corner reflector of T. E. H. Gray et al, in U.S. Pat. No. 3,103,662; the inflatable passive satellite framework of H. E. Henjum in U.S. Pat. No. 3,327,308; and the wire-film space satellite of E. Rottmayer in U.S. Pat. No. 3,354,458.
None of the above patents disclosed reflecting arrangements affording the advantages of dual spectrum capability, signal interference freedom, tangible satellite reflector mass and other advantages of the present invention.